The present invention is in the field of head or helmet mounted reticle and display systems. More specifically, it is a system which provides an image superimposed on the normal field of view of an observer to whose head is has been attached. It is particularly suited to reconnaisance or weapons-aiming applications.
Prior art visual indicating or display systems are typified by the system disclosed in U.S. Pat. No. 3,291,906 to J. J. Ward et al. In the figure of the Ward et al. patent, a multiple gun cathode ray tube is used as source together with a collimating lens system and planar beam splitter. The planar beam splitter is placed in the pilot's line of sight so that the image from the cathode ray tube may be superimposed on the normal scene observed by the pilot.
In prior art development of a system in which these optics may be head-mounted, the cathode ray tube and heavy collimating lenses have been placed in a cylinder and mounted on either the right or left side of the pilot's helmet. This lopsided weight placement is a considerable disadvantage from the pilot's standpoint.
Furthermore, the combiner traditionally used is a small planar eyepiece placed in close proximity to the pilot's eye. This eyepiece is a considerable distraction to some pilots. The close proximity of the eyepiece to the pilot's eye has also been shown to cause pilot anxiety.
Since the prior art uses a beam splitter in combination with collimating optics, the field of view is limited severely by the size of the collimating optics. By using the inside surface of a head-mounted visor as the primary optical element, the field of view of the helmet mounted display apparatus may be significantly increased.
Another disadvantage of prior art helmet mounted display apparatus was that two complete sets of collimating optics were required in order to provide a system utilizable with either eye. The present invention may be used with either eye merely by simple adjustment.
Applicant's invention overcomes these prior art disadvantages by providing a reflective surface on a semi-transparent visor as its primary optical element. The visor is symmetrical about the helmet's longitudinal axis; therefore, no lopsided weight need be attached to the pilot's helmet. Secondly, because the pilots are accustomed to use of a visor and the visor edges are out of the field of view, the anxiety common with the use of a small beam splitter located close to the pilot's eye is averted. Thirdly, since the primary element is a concave mirror, the field of view of the device may be larger. Finally, by placing an adjustable source in the vicinity of the focal point of the inside visor surface the helmet mounted display may be used with either or both eyes.
It is therefore one important object of the present invention to provide head or helmet mounted display apparatus providing superimposed images for either eye without adjustment of the combining surface.
A second important object of applicant's invention is to provide helmet mounted display apparatus whose presence in the pilot's line of sight will not create a distraction to the pilot.